Electricity meters are used to measure electricity consumption for many purposes, including billing for the usage of energy. In many cases, an electricity meter merely keeps track of accumulated energy usage. The accumulated usage over a month is then applied to one or more billing rates (e.g. dollars per kilowatt hour) to arrive at the amount to be billed to the customer for the month.
Other billing methods are employed in other cases. Two common alternative billing methods include so-called Time of Use (TOU) and Demand metering. Time of Use metering involves application of different rates to energy usage at different times of day. To this end, a TOU meter may maintain several accumulators, one for each billing rate. During billing accumulated energy usage is added to the appropriate one of the many accumulators, depending on the time of day. Different billing rates are then applied to the accumulated energy usage values in each of the accumulators. Demand metering involves billing based on time periods in which the demand is at or near a maximum level. Such billing/metering methods are known.
Historically TOU and Demand functions have been performed by the end device (i.e. the meter). Industry standards, and in some cases governmental regulations, require relatively accurate determination of the start and finish of time periods used for TOU and Demand operations. Such accuracy can be achieved by referencing the timing off of the 60 Hz power line signal, which is generally fairly accurate. In such cases, however, power line timing information is lost in a power outage, and there must be some ability to recover chronological time information (time of day) after the power returns.
The problem of recover after a power outage can be addressed by including a clock chip and a battery for power to maintain the time during a power outage. In some cases, the clock chip may be used during normal operation as well. There are disadvantages to reliance on the clock chip for timing information, however, which are outlined below:                1. The accuracy of clock chips drifts over time, causing devices to become out of synch with the real or actual time;        2. Updating the time information in the meter often requires a visit to the physical location with a programming device;        3. Even when the time information is updated in the meter, the programming devices also have clock drift, and as a result, meters across the population on a system are never truly set to the same time base;        4. The cost of a clock chip and a battery is borne by all metering devices in the system.        
To address these problems, some meters now implement two-way communication systems that offer the ability to provide accurate timing information to the meters from a single accurate time base. Keeping the metering devices time synced to the system time greatly improves the accuracy of billing demand and TOU data from the metering devices. However, this solution also has disadvantages. In order to ensure accuracy, all devices must get the correct time within seconds to maintain the integrity of the time-of-use, demand or load profiling data, which is not practical in a system with many metering devices.
There is a need, therefore, for a metering system that addresses one or more of the shortcomings identified above in connection with prior art solutions.